Research On Miniature Single-grating Displacement Measuring Technology With Nanometer Resolution

Nanometer displacement measuring systems are necessary in many fields, such asbio-pharmaceuticals, microelectronics, ultra-precision machining, space science andmaterials science, etc. Displacement measuring technology by grating interferometry,which is one of the technologies that can implement displacement measurement withnanometer resolution, has the advantage of small volume, low cost, simpleconfiguration, being instrumented easily. Aiming at realizing the displacementmeasuring system by grating interferometry with nanometer resolution, the dissertationpractises the in-depth research about the basic principle, key technology, overall design,system realization and performance test of the displacement measuring technology bygrating interferometry. The concrete works and innovative ideas achieved in thisdissertation are concluded as follows.1. The basic principle of displacement measurement with grating interferemeter areintroduced at first. Then the optical subdivision methods in displacement measurementby grating interferemetry are investigated. The interference fields of the diffractive lightare deduced and simulated, and the four-quadrant detecting method and heterodynemeasuring technology are combined to realize the detection with high signal-to-noise.For the two orthogonal signals that gotten, a new approach for phase measurementbased on anti-tangent transformation is proposed. This method divides the phase intotwo parts, one is the integral part, and the other is the decimal part. The exactmathematic expression of the phase is exhibited after the religious deduction. Thisapproach can measure the displacements for both moving directions, and it can reach ahigh precition.2. A miniature single-grating displacement measuring system with nanometerresolution is developed. The overall design of the system is carried out from both theminiature and the nanometer precision points. The semiconductor laser, reflexiblediffractive grating, half-reflecting mirror and reflector are utilized to form the compactoptical configuration. The systemic setting is constructed with the self-manufacturemetal components. The circuit part of the system is accomplished with thefour-quadrant detector and the DSP chips. Then the optical part, the mechanical part andthe circuit part are integrated together, and the single-grating displacement measuringsystem with nanometer resolution is realized.3. The functional test of the designed miniature single-grating displacementmeasuring system with nanometer resolution is implemented. With the help of thehigh-precision capacitance displacement detector and the digital translation stages, theperformance of the system is tested under different intervals, different movingdirections, different moving velocities, different fixed places of the capacitance detectorand different measuring ranges. The results show that the accuracy of the system is improved with the increace of the interval, and it can reach the same level at thedifferent moving directions. Meanwhile, the system reveals a great agreement withdifferent measuring ranges. The disadvantage of the system is that the accuracy maybedecreases when the moving velocity is speeded up.4. The single-grating displacement measuring technology with fiber coupler isinvestigated. The single-grating displacement measuring systems with1×2fibercoupler and2×2fiber coupler separately are developed. The effect of the spoilage forthe output phase difference is analyzed. The functional test of the single-gratingdisplacement measuring system with fiber coupler is implemented. The results revealthat the single-grating displacement measuring system with fiber coupler potentialachieves higher sinnal-to-noise and more robust performance. It maybe attains moreaccuracy and wider applicability.